1. Field of the Invention
The present invention relates, generally, to filtration aids. A process has been developed to improve polymeric filtration aid performance in the removal of gypsum from phosphoric acid/gypsum slurry.
2. Description of the Related Art
During the process of producing phosphoric acid (for fertilizer), gypsum is formed as a by-product in the 25-45% phosphoric acid solution. This gypsum is filtered out with various types of vacuum filters. Polymeric filtration aids have been used to enhance filtration time for faster production and higher recovery of the phosphoric acid.
The polymeric filtration aids are high molecular weight polymers, of various chemistries and molecular weights specific for various phosphate ores. The chemical class of the polymers that have been used is classified as non-ionic, anionic or cationic in nature.
The normal application of the polymers is by making a 0.5-3% polymer solution and injecting this into the gypsum/phosphoric acid slurry prior to filtration (by vacuum filter). The amount of polymer filtration aid for maximum performance varies with each production facility and ranges from 5-150 ppm (via volume of slurry). The amount of performance improvement by the filtration aid varies typically from 5-70%.